Little is known about population patterns of urinary amino acid (AA) excretion, relationships of dietary intake to urinary excretion of specific AA, and relationships of urinary AA to blood pressure (BP) of individuals. The general aim of this research is to make a major advance in this area, based on data from the INTERMAP Study, an international, cooperative, high- quality 17-sample population study of 4,706 men and women ages 40-59 in four countries (U.S., U.K., China, Japan). Analyses are to assess whether, independent of multiple possible confounding variables, there are significant relationships of dietary protein (total, animal, vegetable) and of dietary specific AA to 24-hour urinary excretion of total and individual AA and related compounds; systolic and diastolic BP of individuals are related to their 24-hour urinary excretion of taurine -- a possible marker of fish protein intake; 1-methylhistidine, 3- methylhistidine, histidine, lysine, anserine (1-methylhistidine- beta-alanine dipeptide) -- reflecting meat protein intake; arginine -- source in cells for nitric oxide (NO), implicated in vasodilation; other urinary amino acids. The study has already collected standardized comprehensive dietary and BP data on all individuals in its 17 samples (four 24-hour dietary recalls/person yielding data on 60+ nutrients, including 19 amino acids, two 24-hour urine specimens/person with data on Na, K, urea N, creatinine, volume; eight standardized SBP/DBP measurements/person; other data). Urinary concentrations of amino acids are to be analyzed chromatographically by high performance automatic amino acid analyzers in the INTERMAP Central Laboratory in Leuven, Belgium. Regression coefficients for AA-BP relationships are to be computed without and with correction for reliability (regression-dilution bias); sample-by- sample with pooling by country, region, and then overall; also by gender; for persons not on antihypertensive treatment; nonhypertensives; those free of a history of recent diet change; by education; et al., to evaluate comprehensively whether urinary AA excretion can add meaningfully to dietary data to give a better total understanding of relationships of dietary protein-AA to BP. These data can aid in developing better dietary recommendations for primary prevention of hypertension, and to shift population BP distributions downward to avoid excess risks associated with present levels, generally above optimal.